CONCORD, Calif. (KRON) -- Mt. Diablo High School was placed on lockdown on Monday morning so police could investigate a staff concern.
The Concord Police Department said the lockdown was a precautionary measure as of 10:30 a.m. The lockdown was lifted by 10:51 a.m.
"There has not been a shooting at the school and no one was seen with a gun," police tweeted.
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